Clan of the Cave Bear sucked as a movie.
I was not enamored with the Lord of the Rings movies either in comparison to the books. It was awful how the characters of some of the main players was changed. Samwise was never mean to Gollum and he never coveted the ring. It also really bothered me how Lord Denethor and Faramir's relationship was bastardized. That said, that book was HARD to read.
One movie that I liked better than the book was "Time Machine" (but the original version)